kafka自学之路--zookeeper中存储结构

1.topic注册信息

/brokers/topics/[topic] :

存储某个topic的partitions所有分配信息

Schema: {     "version": "版本编号目前固定为数字1",     "partitions": {         "partitionId编号": [             同步副本组brokerId列表         ],         "partitionId编号": [             同步副本组brokerId列表         ],         .......     } } Example: { "version": 1, "partitions": { "0": [1, 2], "1": [2, 1], "2": [1, 2], } } 说明：紫红色为patitions编号，蓝色为同步副本组brokerId列表

2.partition状态信息

/brokers/topics/[topic]/partitions/[0...N]  其中[0..N]表示partition索引号

/brokers/topics/[topic]/partitions/[partitionId]/state

Schema: { "controller_epoch": 表示kafka集群中的中央控制器选举次数, "leader": 表示该partition选举leader的brokerId, "version": 版本编号默认为1, "leader_epoch": 该partition leader选举次数, "isr": [同步副本组brokerId列表] } Example: { "controller_epoch": 1, "leader": 2, "version": 1, "leader_epoch": 0, "isr": [2, 1] }

3. Broker注册信息

/brokers/ids/[0...N]                 

每个broker的配置文件中都需要指定一个数字类型的id(全局不可重复),此节点为临时znode(EPHEMERAL)

Schema:



Example:

4. Controller epoch: 

/controller_epoch -> int (epoch)   

此值为一个数字,kafka集群中第一个broker第一次启动时为1，以后只要集群中center controller中央控制器所在broker变更或挂掉，就会重新选举新的center controller，每次center controller变更controller_epoch值就会 + 1; 

5. Controller注册信息:

/controller -> int (broker id of the controller)  存储center controller中央控制器所在kafka broker的信息

Schema: { "version": 版本编号默认为1, "brokerid": kafka集群中broker唯一编号, "timestamp": kafka broker中央控制器变更时的时间戳 } Example: { "version": 1, "brokerid": 3, "timestamp": "1403061802981" }

Consumer and Consumer group概念:

a.每个consumer客户端被创建时,会向zookeeper注册自己的信息;
b.此作用主要是为了"负载均衡".
c.同一个Consumer Group中的Consumers，Kafka将相应Topic中的每个消息只发送给其中一个Consumer。
d.Consumer Group中的每个Consumer读取Topic的一个或多个Partitions，并且是唯一的Consumer；
e.一个Consumer group的多个consumer的所有线程依次有序地消费一个topic的所有partitions,如果Consumer group中所有consumer总线程大于partitions数量，则会出现空闲情况;

举例说明：

kafka集群中创建一个topic为report-log   4 partitions 索引编号为0,1,2,3

假如有目前有三个消费者node：注意-->一个consumer中一个消费线程可以消费一个或多个partition.

如果每个consumer创建一个consumer thread线程,各个node消费情况如下，node1消费索引编号为0,1分区，node2费索引编号为2,node3费索引编号为3

如果每个consumer创建2个consumer thread线程，各个node消费情况如下(是从consumer node先后启动状态来确定的)，node1消费索引编号为0,1分区；node2费索引编号为2,3；node3为空闲状态

总结 ：
从以上可知，Consumer Group中各个consumer是根据先后启动的顺序有序消费一个topic的所有partitions的。

如果Consumer Group中所有consumer的总线程数大于partitions数量，则可能consumer thread或consumer会出现空闲状态。

Consumer均衡算法
当一个group中,有consumer加入或者离开时,会触发partitions均衡.均衡的最终目的,是提升topic的并发消费能力.
1) 假如topic1,具有如下partitions: P0,P1,P2,P3
2) 加入group中,有如下consumer: C0,C1
3) 首先根据partition索引号对partitions排序: P0,P1,P2,P3
4) 根据(consumer.id + '-'+ thread序号)排序: C0,C1
5) 计算倍数: M = [P0,P1,P2,P3].size / [C0,C1].size,本例值M=2(向上取整)
6) 然后依次分配partitions: C0 = [P0,P1],C1=[P2,P3],即Ci = [P(i * M),P((i + 1) * M -1)]

6. Consumer注册信息:

每个consumer都有一个唯一的ID(consumerId可以通过配置文件指定,也可以由系统生成),此id用来标记消费者信息.

/consumers/[groupId]/ids/[consumerIdString]

Schema:



Example:
{ "version": 1, "subscription": { "open_platform_opt_push_plus1": 5 }, "pattern": "static", "timestamp": "1411294187842" }

7. Consumer owner:

/consumers/[groupId]/owners/[topic]/[partitionId] -> consumerIdString + threadId索引编号

当consumer启动时,所触发的操作:

a) 首先进行"Consumer Id注册";

b) 然后在"Consumer id 注册"节点下注册一个watch用来监听当前group中其他consumer的"退出"和"加入";只要此znode path下节点列表变更,都会触发此group下consumer的负载均衡.(比如一个consumer失效,那么其他consumer接管partitions).

c) 在"Broker id 注册"节点下,注册一个watch用来监听broker的存活情况;如果broker列表变更,将会触发所有的groups下的consumer重新balance.

8. Consumer offset:

/consumers/[groupId]/offsets/[topic]/[partitionId] -> long (offset)

用来跟踪每个consumer目前所消费的partition中最大的offset

此znode为持久节点,可以看出offset跟group_id有关,以表明当消费者组(consumer group)中一个消费者失效,

重新触发balance,其他consumer可以继续消费.

9. Re-assign partitions

/admin/reassign_partitions

{
   "fields":[
      {
         "name":"version",
         "type":"int",
         "doc":"version id"
      },
      {
         "name":"partitions",
         "type":{
            "type":"array",
            "items":{
               "fields":[
                  {
                     "name":"topic",
                     "type":"string",
                     "doc":"topic of the partition to be reassigned"
                  },
                  {
                     "name":"partition",
                     "type":"int",
                     "doc":"the partition to be reassigned"
                  },
                  {
                     "name":"replicas",
                     "type":"array",
                     "items":"int",
                     "doc":"a list of replica ids"
                  }
               ],
            }
            "doc":"an array of partitions to be reassigned to new replicas"
         }
      }
   ]
}

Example:
{
  "version": 1,
  "partitions":
     [
        {
            "topic": "Foo",
            "partition": 1,
            "replicas": [0, 1, 3]
        }
     ]
}

10. Preferred replication election

/admin/preferred_replica_election

{
   "fields":[
      {
         "name":"version",
         "type":"int",
         "doc":"version id"
      },
      {
         "name":"partitions",
         "type":{
            "type":"array",
            "items":{
               "fields":[
                  {
                     "name":"topic",
                     "type":"string",
                     "doc":"topic of the partition for which preferred replica election should be triggered"
                  },
                  {
                     "name":"partition",
                     "type":"int",
                     "doc":"the partition for which preferred replica election should be triggered"
                  }
               ],
            }
            "doc":"an array of partitions for which preferred replica election should be triggered"
         }
      }
   ]
}

例子:

{
  "version": 1,
  "partitions":
     [
        {
            "topic": "Foo",
            "partition": 1
        },
        {
            "topic": "Bar",
            "partition": 0
        }
     ]
}

11. 删除topics
/admin/delete_topics

Schema:
{  "fields":
    [ {"name": "version", "type": "int", "doc": "version id"},
      {"name": "topics",
       "type": { "type": "array", "items": "string", "doc": "an array of topics to be deleted"}
      } ]
}

例子:
{
  "version": 1,
  "topics": ["foo", "bar"]
}

Topic配置

/config/topics/[topic_name]

例子

{
  "version": 1,
  "config": {
    "config.a": "x",
    "config.b": "y",
    ...
  }
}